The god of sorcery, Magnus withdrew from the creation of the world at the last second, though it cost him dearly. What is left of him on the world is felt and controlled by mortals as magic. One story says that, while the idea was thought up by Lorkhan, it was Magnus who created the schematics and diagrams needed to construct the mortal plane. He is sometimes represented by an astrolabe, a telescope, or, more commonly, a staff. Cyrodiilic legends say he can inhabit the bodies of powerful magicians and lend them his power. Associated with Zurin Arctus, the Underking. It is said that as he fled Mundus in the last of its birth-pains, he tore a massive hole in the fabric of Oblivion, leading to Aetherius. This hole is Nirn's sun, known itself as Magnus. He was followed shortly thereafter by the Magna Ge who formed the stars.
http://www.youtube.com/watch?v=L5zVawg-J-w&feature=player_detailpage#t=224s
Could http://www.youtube.com/watch?v=JSRtYpNRoN0&feature=player_detailpage#t=22s guy in the trailer (middle one) be Magnus?